Most of the time high temperature sensors consist of an outer sheeting which is exposed to the medium to be measured. More specifically, this is the case with exhaust gas temperature sensors where the outer sheet is in contact with the exhaust gas while the internal temperature sensing element is in contact with an internal medium conducting and transferring the heat-flux from the outside to the inside. The internal temperature sensing element could be a positive temperature coefficient (PTC) thermistor or negative temperature coefficient (NTC) thermistor.
High temperature sensors are affected by very high heating and cooling gradients. The gradients lead to excessive compressive and tensile stresses between several materials of the internal components, connections and leads. The stresses could lead to damage of the internal components and conductors carrying the output signal representing the temperature sensed by the internal temperature sensing element.
U.S. Pat. No. 6,639,505 B2 discloses a temperature sensor wherein the distance between a thermistor element and a metal enclosure is not larger than 0.3 mm and the thermistor element and metal enclosure are in contact with each other via an insulating member. The insulating member may be a crystallized glass or a ceramic. The insulating member eliminates undesired gaps among the thermistor element and metal enclosure.
U.S. Pat. No. 6,829,820 B2 discloses a method of manufacturing a temperature sensor. A thermistor element is inserted into a bottomed metal tube while filling an inside of the metal tube with a filler material, preferably of silicone oil, to reduce a sliding resistance between the thermistor element and the metal tube as an integral temperature sensing structure which is then mounted in a housing. The metal tube is heated after insertion of the thermistor element there in so as to volatize an oil component of the silicone oil. The method reduces the defects due to bending of the electrode wires of the thermistor during placement of the thermistor in the metal tube.
In the temperature sensors described above stresses on the conductors caused by changes in temperature and vibrations between the measurement resistor and the supply-line cable lead to wear on the conductors. In U.S. Pat. No. 8,328,419 B2, a solution to this problem is disclosed. Heat-decoupling wires are arranged between the measurement resistor and strands of the supply-line cable. The heat decoupling wires are stuck as spiral springs on the strands of the mineral insulated supply line cable and connect elastically the measurement resistor to the supply-line cable.